On the PTR, as far as I can tell, there is nothing in the character selection screen, or server list that indicates who is grouped with who. The only way to tell is if I see someone at the Shrine that is from another server.

This is a problem, because I could be grouped with a very low pop server, but may never know it because it could be once in a blue moon that someone from that server is actually around. Seeing someone on a low pop realm is like a rare mob.